Synthetic rubber



E. E. ASTAHLY Filed Nov. 22, 1954 l) n v l l?) (swoaJ/u ,w 3mm u, 9 INVENTOR HJ so )lava/.J JA/Ozo E Do/v E. .S7/wz y,

BY 7M 7 ATTORNEY March 24, 1964 United States Patent() COMPOUND N,N'DI(3,5,5-TRMETHYLCYCLO- HEXYD-p-PHENYLENEDIAMINE Eldon E. Stahly, Grosse Pointe, Mich., assignor, by direct and mesne assignments, of three-fourths to Oliver W. Burke, Jr., Grosse Pointe, Mich., and one-fourth to Eastman Kodak Company, Rochester, N.Y., a corpora- 'tion of New Jersey Filed Nov. 22, 1954, Ser. No. 470,401 1 Claim. (Cl. 260-577) The present invention relates to a new class of valuable antiozidants for vulcanizable elastomers such as natural rubber and synthetic elastomers such as polybntadiene7 GR-S type synthetic rubbers, and other diene vinyl copolymers such as acrylonitrile-butadiene elastomer, etc. The said class of antiozidants is also effective as antiozidants for use in non-vulcanizable elastomers, plastomers and resins, particularly those which have residual unsaturation.

It is Well known that many compounds possess the property of preserving rubber, when incorporated therein, against attack by oxygen, light and heat. Such compounds are termed antioxidants. However, the attack by ozone, up to the time of the present invention, has been a problem not solved by the known antioxidants. The present invention aims to provide specific new materials, ingredients, or additives, which protect rubber against deterioration by ozone attack, especially after subjection of the rubbers to elevated temperatures, and which are substantially non-toxic, and have other advantages as Well.

The problem of ozone attack on both natural and synthetic rubber goods is of high importance to both civilian and military consumers.

As early as 1944 the ASTM prescribed testing procedure for measuring ozone attack in connection with essentially static goods, such as refrigerator gaskets, windshield mountings and the like. It has more recently been determined that when dynamically flexed rubber goods, such as tires, are made in the usual way, with or without antioxidants, such articles are subject to deterioration by ozone attacks, Whether in continuous or intermittent use or in storage. This ozone attack on statically or dynamically employed rubber goods becomes apparent by the development of penetrating cracks which progressively become deeper with time of exposure to the atmosphere, which practically always contains ozone in trace amounts. Such cracks in tires often becomes sufliciently deep to cause failure. Indeed, in the case of new tires stored for substantial periods, such cracks may cause failure within a relatively short time after the tires are put into use. This result of ozone attack is thus quite distinct from the development of ne surface cracks, i.e., checking and crazing, resulting from oxidative deterioration.

Ozone attack is extremely bad in areas indigent to cities, such as Los Angeles, California, where smog conditions are associated with high ozone concentrations, e.g., above l parts per hundred million. In Los Angeles and similar high-ozone areas so-called ozone cracks may develop in rubber articles such as tires in less than a month of storage time. In areas such as Detroit, Michigan, the normal ozone concentration in the air is less than parts 3,125,412 Patented Mar. 24, 1564 per hundred million, and ozone cracks may not develop for several months.

In any event ozone-cracking is recognized as one of the heretofore important unsolved problems in storage and use of both civilian and military articles containing natural or synthetic rubber parts.

Previous to the present invention the rubber industry has employed chemicals such as Santoex AW (the trade name for 6-ethoxy-2,2,4-tri-methyl-1,2-dihydroquinoline) in rubber articles to protect the same against oxidation on aging. From a survey of chemicals used to protect the products of representative manufacturers of rubber goods it appears that Santoex AW has been regarded as one ot' the best materials available for that purpose. Accordingly, to demonstrate the ozone resistance afforded by the new additives of this invention, a GR-S compound containing Santoex AW was compared with GR-S containing other antioxidant materials, to determine which of such materials seemed the most resistant to ozone attack after subjecting to heat aging conditions, and since the Santoiiex AW seemed to be the best of the materials so compared, it was used as a standard for comparison to evaluate the greatly improved resistance to such attacks imparted by the new antiozidants of the present invention. In spite of accepted usage of Santoex AW by the industry it will be noted from the examples cited in Table I, as compared to Tables II and Ill that relatively little protection of elastomers against ozone cracking is afforded by Santolex AW, as compared to the antiozidants of the present invention, after the samples had been heated.

The present research has shown that certain diamines may show some protective action against ozone before the sample has been heat-aged. When stored for long periods at 20 C., or when used for shorter periods in applications at higher temperatures such as are reached in normal usage of automobile or truck tires, the protective action is gradually lost. For example, in Sample 3 of Table Il, before aging, rubber compounds containing N,Ndisec butyl-p-phenylenediamine show protection against ozone cracking at ordinary temperatures, but after heat aging this protection is absent, and such a compound when ernployed in tires, would not protect such tires in use. Thus, protective action after heat treatment is properly taken as a measure of eiciency of an additive as a practical antiozidant.

A requisite property in case of antiozidants, as in the case of any other additives to rubber, is inertness with respect to the curing ingredients of the elastomer compound. The compounds after heat aging (24 hours at C. is taken as an exacting standard herein) should still show about 275 or greater elongation to be suitable for tire stocks. Original and heat-aged stress-strain properties were therefore both obtained and are included in the tables of data herein. Certain compounds such as benzidine resulted in a Very short stock after aging (see Examples 1 32, I-33 and l-36) While protection against ozone was good, such additives caused over-curing, thus rendering them unsuitable for use in GR-S stocks for manufacture of tires and many other articles of commerce.

Thus, principal objects of the present invention are (l) the provisions of the new chemical compounds for incorporation into elastomer and plastomer compositions which will effectively protect the same against ozonecracking especially after aging or heat aging Without deleteriously altering the physical properties of the protected materials, and (2) the provision of elastomer and plastomer articles including such chemicals and rendered ozone resistant thereby.

This invention resides in the (1) new and useful chemical compounds, (2) the incorporating of such compounds into high polymeric materials and latices of such polymeric materials, and (3) the products resulting therefrom, as is herein disclosed and as is more particularly pointed out in the appended claims.

The new materials of this invention herein termed antiozidants, which have been found highly eiective for protection of high molecular weight compounds against attack by ozone, are members of a class consisting of substituted p-phenylenediamine in which at least one amino group is a secondary amino group substituted with a radical selected from the class consisting of a secondary alkyl radical and alkyl substituted cycloalkyl radical, and in which the sum total of the hydrocarbon substituent carbon atoms present lies within the range of not less than 16 and not more than 26 and further this invention includes the incorporation of these new chemical compounds into high polymeric materials and the products therefrom.

For simplicity of production it is preferred that each amino group is secondary and that the substituents of the substituted p-phenylenediamine are secondary alkyl groups and that each comprises the same number of carbon atoms within the limits of 8 to 13 carbon atoms.

The appropriate incorporation of the new antiozidants gives virtual immunity against much higher than ordinary atmospheric concentrations of ozone to elastomer cornpositions even when the same have been subjected to radical heat aging, thus showing that these antiozidants are capable of protecting the products for long periods of time in geographical areas of low ozone concentration, i.e., less than parts per hundred million.

The new compounds for this invention may be prepared in a simple manner by aminative reductions of ketones with p-phenylenediamines and hydrogen. For example, one mole NH2C6H4NH2 plus 2 moles diisobutyl ketone plus hydrogen with a hydrogenating catalyst, such as copper chromite or Raney nickel, under the influence of heat and pressure, produce N,Ndisecondary nonyl derivatives of the diamine, namely,

The above reaction can be run with one mole of p-phenylenediamine so that the iirst produce contains and this product can be further treated with a second alkyl ketone to effect substitution in the second amino group. There are other practical methods of preparation, and this aminative reduction method is mentioned as illustrative only.

The research has shown that the new compounds are valuable antiozidants for plastomers and resins as well as for natural and synthetic rubbers and are particularly useful antiozidants for tires and like natural and synthetic products subject to ozone attack at high operating temperatures, such as those temperatures attained by heavy duty truck tires, and such temperatures may even rise to 300 F. in use. Anitozidants are herein dened as additive agents which protect the polymeric material, e.g., natural and synthetic rubbers, against deterioration due to ozone attack. While serving an antiozidants, the new compounds also serve as antioxidants, i.e., the new products of this invention protect against crazing and the development of small tine superficial surface cracks in rubber compounds due to attack by oxygen and sunlight. The new compounds are specific and diifer from diaryl amines, dialkyl amines, arylenediamines, and their derivatives, in general, in that other members of these general categories will not eiectively protect against attack by ozone as is demonstrated by the research summarized hereinafter in Table I.

PREPARATION AND TESTING PROCEDURES The procedures employed in compounding and testing the elastomeramino-additive compositions for the examples of Tables I, II and IV herein was as follows: as control samples cold GR-S synthetic rubber (GR-S 1500 polymerized at 41 F.) was compounded and vulcanized according to best known commercial practice to obtain good aging properties. Then similar compounds were prepared and vulcanized with our new antiozidants present as additives. The recipe employed for the control compound was as follows:

Parts by Components: weight GR-S 1500 HAF carbon black 40 to l50 EPC carbon black Oto 10 Zinc oxide 3 Stearic acid 1 to 3 Phcnylbetanaphthylamine l to 1.25 Circo Light Oil 1 2.5 to 3.5 Para Flux 2016 1 2.5 to 3.5 Sunproof or Heliozone Wax 1 to 1.5 Santocure (accelerator)2 1.0 Sulfur 2.0 Santoflex AW 2.0

lCommercial plasticizing oils (see book entitled Colnpounding Ingredients for Rubber, published 1947 by India Rubber World, New York, N.Y.).

ISantoeure is the trade name for N-cyclohexyl-Z-benzothiazole sulfenamide.

The compounding formula for the natural rubber specimens is appended to Table III, following.

When compounds were prepared with the new antiozidants or with other antiozidants or additives, the Santoflex AW was omitted in the above recipe and the new antiozidants or other materials were used in its place.

The synthetic and natural rubber samples were cured at about 1000 p.s.i. in a steam heated press at 85 F. with curing times adjusted in the range from 30 to 120 minutes, as required to obtain optimum tensile properties for each specific compound. Samples of each of the cured stocks were heat aged for 24 to 4S hours at 100 C., and were then subjected to ozone exposures in both dynamic and static tests.

The dynamic ozone test was conducted on 1/2 inch dumbell specimens of the vulcanizates. The exposure to ozone was carried out in an aluminum lined ozine cabinet where the concentration of ozones was usually held at 25i5 parts per hundred million of air. This high ozone concentration is used as specified by ASTM test D-l 14'9-51T to accentuate the protective etect of the additive antiozidants in a reasonable short time of evaluation. Occasionally more highly accelerated ozone exposure tests were conducted by employing ozone concentrations as high as p.p.h.m. With such high ozone concentrations much shorter times are required to obtain valid comparisons of the protective action of the additives under test (e.g., Table I, Examples 21 to 30 inclusive). The sample was stretched and relaxed continuously at a rate of 30 times per minute, between 0 and 20% elongation, to simulate conditions of dynamic use of the rubber. After each test usually of three days duration, a specimen taken from the center part of the narrow part of the dumbell was placed under the microscope and the depth of the observed cracks was measured.

The depths ofthe deeper 50% of the observed cracks were averaged, and this average Was designated as the A Value and was taken as the index of ozone attack. With each experimental sample a control sample containing Santoflex AW was simultaneously subjected to the same 6 synthetic rubber against ozone attack, either before or after the GR-S vulcanizate was subjected to accelerated aging at elevated temperatures. However, they belong to one or more classes of materials known to have antioxidant properties. Because Santolex AW is highly redynamic ozone test, and the average crack depth, A gaided in the industry, samples containing it were tested value, was compared with the A value for the crack with each group of samples containing other amino comdepths of this control sample, as a basis of evaluation. pounds to monitor the procedure and to give assurance The static tests (Table IV) were run on both heat that the several results were valid for evaluating theaged and unaged samples. Dumbell specimens were relative effectiveness of the several amino compounds for mounted in accordance with ASTM procedure D518-44, protection of GR-S against ozone attack.

Method B. The mounted samples were placed in the Ortho and meta-diamino aromatic compounds are relaozone exposure cabinet wherein the ozone concentration tively inactive as antiozidants (Table I, Examples 79, V80,

was held at a concentration of i5 p.p.h.m. at a tem- 184, and 185); also certain compounds, e.g., naphthylperature of C. In this static test the samples were 15 amine and tetrahydronaphthylamine derivatives, although observed periodically and the time was measured to the good antioxidants, are not good antioxidants. (See appearance of the rst crack. The run was continued Table I, Samples 161 and 163.) Y

to obtain relative ratings on rate of crack growth and A Study of Table I is suieient to eonrm that most fatll'lgs Were heI1 3PP11d 011 the bISIS Of the ASTM lattypes of amino-antioxidants are of little or no value in 111g System Shown 1n Table V- 20 Vvcompounding elastomers to make ozone-resistant articles` Table V of use. Certain compounds show some protection Aagainst ozone in Vcomparison with Santoex AW, e.g., Examples Rating: Developments in static tests 20 and 186, but after heat aging protectionragainst ozone 0 No developments of any kind. r was not outstanding. It should also be called to atten- 1 Microscopic cracking. 20V tion that the GR-S 1500 examples herein contained from 2 Fine visible cracking. A 1 to 1.25 parts of plienylbetanaphtliylamine (PBNA) 30 the industrial plants producing GR-S Vto protect against OBSERVED RESULTS Y oxidation during shipment and storage. It doesrnot Table 1 lists many amino compounds, diamino` c0111. protect compounded and cured articles produced therepounds, polyamino compounds and derivatives thereof from against ozone cracking (see Examples I-l and which showed very poor protection of vulcanized GR-S I-101).

Table I OZONE ATTACK oN GR-S 1500 WITH VARIOUS AMINES INCLUDED IN THE COMPOUNDING RECIPES As DETERMINED BY DYNAMIC ozoNE TEST1 Crack depth Agedproperties A Value in Y 300% Pecent Y Y microns Example Code number Amine compound (pts/ pts. elastomer) Tens. mod. eiong.

l Tens. Percent Un- Heat elong. aged aged GROUP A i Control (GR-S 1500 with no added amine) 2, 710 1, 820 450 Santoflex AW 2 (5) (2nd Contro1) 1, 330 430 Santoex AW 2 (2) (3rd Contro1) 970 610 Reaction product; of 1, 4-cyclohexanedione-l-aniline-t-Hr (5).. 2, 460 1, 640 450 Tetrah droquinoline (2.5) 3,320 ,670 505 Piperi iniumpentametliylenedithioearbamate (2.5) 1,810 270 Bis (p-amiriophenyi)-4-amino-m-tolylcarbi1iol (5).- 2,590 1, 840 410 Sairanin O (5) (3,7-dimethylphenosairanine) 2,330 295 Phenosafranin (5) 3,150 2,430 885 Santoflex AW 2 (2) (Control) 2, 350 970 610 Laetonitrilo-p,p'diami1iodiphenylmethane (5) 2, 730 2, 140 375 Phenyl-1,2,3,4tetraliydro-2-naplithylamine (5)...- 3, 110 1, 890 440 1,2,3,4-tetrahydro-Z-naphthylamine 2, 840 2, 090 375 Di-see-butylphenylenediamjne (2.1)-l-rosin acid (10.6)- 2,640 1,080 585 4,4,4"-triamjnotriphenylmethaiie(5) 2,790 2,180 350 letraethylthiuramdisulde (2.5)-. 2, 590 285 1,4-Bis(1,2,3,Metrahydro-2-naphthylamiuo) benzene (5) 990 1, 820 455 santonex AW 2 (2) (Control) 2, 350 970 610 2,270 A280 200 545 N,N'-di-seo-butyi-p-pnenyienediamine(2.5)+rosinaeid(0 3,300 1,800 475 2, 870 245 250 61o N,Ndi-sec-butyl-p-phenylenediamine-ZBF3 complex (5) 2,940 1,720 500 2,910 250 0 Y 335 Santonex AW2 (2) (Control) 2,350 970 610 2,270 280 430 Tri-n-butyiamino (5) 3,250 1,950 465 2,120 175 525 p-Ammobenzoio acid (5)- s, 020 1,760 490 2,330 17o 755 Diazoarninobenzene (5) 3,340 3,100 320 2, 530 180 740 p,p-Tetramethyldiaininodipheiiyimethane (5) 8, 420 1,770 485 2,570 225 395 2,4,6-tr1s (dimothylaminomethyi) phono1(5) 3, 490 1,880 490 2, 290 170 520 Rosinamine D (25) 1,840 1, 070 415 420 See footnotes at end of table.

Table I-Continued Crack depth Agedproperties "A Value in 300% Percent microns Example Code number Amine compound (pts./100 pts. elastomer) Tens. mod. elong.

Tens. Percent Un- Heat elong. aged aged GROUP E 28 G-2541 Santolex AW (2) 970 610 2, 270 280 N,Ndiphenyl-p-phenylencdiamnc (5) 2, 350 420 2,940 235 p,p-Diaminodiphenylmethane (5) 3, 200 2, 370 395 1, 630 70 Santoex AW 2 (2) (Control) 2, 350 970 610 2, 270 280 185 500 N ,N-disecbutyl-p-phenylenedlamme (2) ,480 2, 290 435 2, 640 195 100 410 Benzidne 3,010 2, 550 365 2, 150 110 80 100 N, Ndi-sec-butyl-p-phenylenediamine (2) Castor oil (12.5) 3,080 2,110 405 2,220 160 100 +Dresinate 731 acids (12.5).

Santoex AW2 (2) (Control) 2, 700 1,500 510 Benzidino (2H-Rosin (6,5) 3, 500 2, 290 455 1,860 75 Quinoline 3, 070 ,820 325 2, 050 145 p'-Bis(2,5-dimethylpyrro1idiny1)biphenyl (5) 3, 380 2,340 415 2, 100 115 ,Ndi(1-phenylethy1)benzid1ne (5) 3, 380 2, 050 465 2, 760 200 Santotlex AW (2) (Control) 2, 350 970 610 2,270 280 1,2,3-triphenylguanidlne (5) 3, 290 2, 550 375 2, 170 Y 170 n-Butyl-p-aminophenol (5) 2,610 1, 040 650 2, 460 260 Mono-oleic amide of pphenylenediam1ne (5) 2, 800 1, 370 530 Uns-N,N-dioyclohexyl-p-phenylene-diamure (5) 2, 740 2, 040 425 santooex AW (2) (Control) 2, 35o 97o 61o 2, 270 28o Alkylamine JM-R (5) 2,180 370 2, 040 175 Benzidine (solubilized) (2,5) 2, 250 375 1, 640 100 Dioyclohexylammonum nitrite (5) 2, 940 560 345 2, 560 185 GROUP J 49 G-3414-2 Santoex AW 2 (2) (Control) 2,350 970 610 2, 270 280 130 50 E-89 Phenothiazine (5) 3,110 2, 070 435 2, 390 170 110 GROUP K Santoilex AW 2 (2) (Control) 2,350 970 610 2, 270 280 510 N,N'-di-seo-butyl-p-phenylenediamine (3H-PENA 3 (3) 2, 600 1, 970 410 290 N,Ndi-sec-butyl-p-phenylenediamine (4.65)-i-PBNA 3 GROUP L 54 (3f-3414 Santo'lex AWE2 (2) (Control) 2, 350 970 610 2,270 280 115 500 55 F-25 Reaction product of N,Ndi-sec-butyl-p-phenyleuediamne 070 1, 120 595 2, 650 310 20 310 and laotonitrile (1:1 mole ratio) (5). 56 F-26 Reaction product of N,N-dsec-butyl-p-phenylenediamine 3,000 1, 460 545 2, 980 285 0 320 and lacnitrile (2) and tetraethylenepentamine mole ratio 112:1) 57 E-33 Mono-oxalate of N-Nd-seo-butyI-pheuylenediamine (5)...- 3,250 1, 950 475 2, 720 215 0 380 GRoUr M Santoex AW 2 (2) (Control) 2, 350 970 610 2, 270 280 1naphthylamine4,8disulfonic acid (sodium salt) (5).. 3, 280 2,010 485 2, 530 185 2naphthylamine4,S-disulfonic acid (5) 3, 110 2,010 485 2, 530 185 2-napht11ylamine-1-su1fonio acid (sodium salt) (5). 3, 420 2, 530 405 2, 310 170 Dlmethylaminomethylphenol (5) 3, 350 l, 840 475 2, 340 165 o-Dimethylaminoethyl-p-butyl-phenol (5) 3, 540 2, 150 435 2, 530 160 o-Dimethylaminoethyl-p-octyl-phenol (5)... 3, 630 2, 050 455 2, 370 175 4,4 -diamin0-2,2biphenyld1sulfonic acid (3.5) 3, 460 1, 780 510 2,840 235 p,pJletrarnethyldiaminobenzophenone (5). 3, 680 1, 840 490 2, 930 275 p,p-Diamnodiphenylamine (2) sulfonic acid 3, 510 2, 350 420 2, 940 235 Santoex AWZ (2) (Control) 2, 350 ,950 475 2,720 215 Octadecylamne(5)-i-montmorllonite (13). 2, 840 1, 240 525 2, 400 245 Dimethyldoctadecylammonium montmorillonite (9) 2, 940 2, 460 355 2,400 185 Rosinaminc D (5)-f-kaolln (13) 2,970 1,360 505 2, 670 305 Rosinarnine D (5) +montm0rll0nitc(13) ,260 1, 260 560 2, 520 290 Santoflex AW2 (2) (Control) 2, 350 970 610 2, 270 280 p-aminoazobenzene (5) 3, 190 2,340 395 2,900 210 N,Ndisce-butyl-p-phenylcncdiamine (2) 2, 990 ,890 435 2, 370 150 2,4,6-triaminotoluene (2) 2, 810 1,670 455 2, 340 120 1,3,5-triamn0benzeue (2). 3,110 1, 930 440 1,550 65 Phloramine sulfate (2) 2, 500 1, 310 505 1,680 75 m-Phenylcnediamine(l)-1rosin(5.) 2, 990 1, 840 445 2, 070 100 o-Phenylenediamine(1)+rosin(5.6) 3, 090 l, 650 485 2, 190 130 p-Phenylenediarnine(1)+rosn(5.6) 2, 690 2, 380 335 1, 510 85 N-nitrosodiphenylamine (5) 2,490 1, 060 615 2,390 150 N,Ild-sei-bltyl-p-phenylenediamine (2.85) and montmo- ,130 310 875 1,800 245 ri onite 26 Benzdine (2.4) and montmorillonite (26) 1,250 490 705 1,905 205 Phenylbiguanide (5) 210 1, 800 365 2, 230 230 'See footnotes at end 0f table.

Table l-Continued Crack depth Agedproperties A Value in 300% Percent microns Example Code number Amine compound (pts./100 pts. elastomer) Tens. mod. elong.

Tens. Percent Un- Heat elong. aged aged Santolex AWz (2) (Control) 2, 350 970 610 2, 270 280 2,6-diaminopyridine 1, 580 650 610 2, 050 365 2famnopyridine (5) 2, 730 2, 440 325 2, 350 185 Santolex AW2 (2) (Control) 2, 350 970 610 2, 270 280 Quinaldine (3) 2, 940 2, 230 390 2, 300 165 Phenyl-beta-naphthylamine (1) 3,100 2, 120 365 i 960 155 Santoflex AW2 (2) (Control) 9, 990 595 2,270 280 120 Diacetylbenzdine (5) 1, 860 465 2, 750 180 360 substituted dihydrazide oi adi ic acid (2)- 2, 320 425 2, 560 185 280 Substituted pyrazolinylazine 2) 3, 560 2, 010 475 2, 440 195 230 Santoilex AWl (2) (Control) 2,320 990 Crude p,pbis(dlmethylpyrroldnyl)biphenyl (5)- 3, 350 2,050 Flectol H 4 (5) 3, 210 2,140 Santoflex B 5 (5) 3, 470 2, 120

Santoex AW 1 (2) (Control) 2, 350 790 Hydrobenzamide (5) 2, 070 Auramine hydrochloride (5) 2,910 2, 700 2-an1lino-1,4dipheny15phen 3, 330 2, 440 Tetrahydrophthalimide (5) 2, 760 2, 220 2,4-diamlnoto1uene (5)-- 2, 590 990 Isatin (5) 2, 820 1, 410 4-aminoantipyrine (5) 2, 770 1, 780 4,4-diaminodiphenyl sulfon 3, 240 2, 030 Rosaniline hydrochloride (5) 2,800 2,050 Polyamide resin 94 (10) 2, 570 1, 530 Aurin (5) 2, 870 1, 910

Santoex AW- (2) (Control) 2,350 970 N icotinic acid (5) 2, 700 2. 010 Polyvinylpyrdine (10) 2, 550 2, 200 p-Diazodphenylamjne sulfate (2)- 3, 390 2, 350 Bcnzidine-2, 2disulxonic acid (2) 2, 570 2, 130 Citriazinic acid solubilized in tri- 3, 350 2, 330

hydroxide (2.5). Citrazinic acid (2.5) 3, 200 1, 860 Diphenylamine (5) 3, 140 2, 230 Azoxybenzene (5)- 3, 110 2, 370

Santolex AWn (2) (Control) 2,350 970 Reaction product of lactonitrile and iurfurylarnine 710 1, 020 Reaction prodruct of lactonitrile and 12-15 carbine am 920 1, 620 Reaction product oi lactonitrile and 18-24 carbon amine (5) 3,120 1, 800 Tris (hydrozxy'methyDaminomethane (5) 2 83 2, 180 2-aminobenzwnethiol (5) 1, 760 Phenylhydrazine (5) l, 140 5, 5-dimethyl-hydantoin (5) 1, 930 Dimethyl-p, pezodibenzoate 2, 440 4-arnno2, -dimethylpyrimidine (5) Hydrazobenzene (5) 2,480

Santoex AW2(2) (Control) 2, 350 970 610 2, 270 280 Benzidne (2.5) Y 3, 000 1,200 600 2,280 280 No additive 3, 000 1, 200 570 2, 2'-diethy1dihexy1amine (5). 1,380 210 1, 160 110 2-py'1'r01done (5). 2, 970 2, 770 325 2, 540 190 N -vinyl-2-pyrrolidone (5) 3, 050 2, 240 400 2, 630 215 GROUP z G-34141 Santoiex AW (2) (Control) 2,350 970 610 2, 270 280 E-27 Reaction product oi benzidine and lactonitrile (1:1) (5) 2, 800 1, 990 435 2, 320 190 E28 Reo2t io r product of p-phenylenediamjne and lactonitrle 1, 900 1, 080 480 2,110 275 E-29 eacfgio) product of p-phenylenediamine and lactom'trile 2, 730 1, 630 465 1, 900 195 1:1 E-30 Alpha-isopropylaminopropiontrile (5) 3, 000 2, 270 385 2, 200 182 410 E-32- p-aminodiphenyl (5) 3, 300 2, 180 440 2, 730 205 230 See footnotes at end of table.

Table l-Continued Crack depth Agedproperties A Value" in 300% Percent microns Example Code number Amine compound (pts/100 pts. elastomer) Tens. mod. elong.

Tens. Percent Un- Heat clong. aged aged GROUP AA Santoex AW2 (2) (Control) 2, 350 970 610 2,270 280 155 Bcnzidine monobxalatc (5) 3,170 2, 030 435 2, 290 145 395 Pyridine-boronfiuoride complex (5) 3, 130 1, 600 527 2, 620 190 400 Z-aminothiazole (5) 2, 520 1, 920 375 2, 400 200 305 Reaction product of benzidine and crotonaldehyde (1:1) (2.5). 2, 870 2, 490 340 l, 890 140 250 1 cyolohexylamino2-propanol (5) 2, 920 1, 960 405 2, 530 250 205 React)ion)product of lactonitrile and m-Phenylenediamine 2, 680 1, 230 590 2, 710 275 345 (1:1 (5. Reaction product of lactonit-rile and m-Phcnylenediamine 1,420 490 665 2,320 435 565 (2. 2aminobenzothiazole (5) 3, 000 2, O40 410 2, 400 200 290 Santoiex AW2 (2) (Control) 2,350 970 610 2, 270 290 205 Polymethacrylamide (5) 2. 990 1, 680 475 1, 750 155 460 Urea (5)... 2.600 245 2,220 120 Broke Naphthylamine (5) 1, 3-dipheuyltriazene (5) N, N/ diphenyiethyienediamine (5) 2, 81o 98o co5 2,170 25o 225 GROUP AC G 3414-2 Santoex AW 2 (2) (Control) 2,350 970 610 2,270 290 195 E-70 Polyester of dilinoleic acid and ethyleneglycol (10) benzi- 2,510 1,060 540 1,810 180 300 E-75 Rfixetnr'ductoftetraethylene pentamine andiactonitrue 1,510 42o 865 1, 95o 445 535 GROUP AD Reilly Tar 819(2.5) alkylamine .TM-R (2.5)- 3,020 2,020 Hydrofuramide (5) 2,850 1,790 N-phenyl-l-naphthylamine (5) 2,130 1, 650 N,Nbis(2-hydroxypropyl)-p-phcnylened1am1ne (5) 3, 260 1, 250

Santoilex AW 2 (2) (ContrOl) 2,350 970 Phenyl-beta-naphthylanune (1) 3, 430 1, 750 Carbazole (5).. 1,900 Aminoacetanilide (5) 2, 120 Tetraphenylhydrazine (5). 1, 730 Duomeen S (5) l 2, 650 1, 530 Sym-di-beta-naphthyl-p-phenylenediamme (5) 3, 330 2, 070 N,Ndi(l-phenylethyDbenzldine (2.5) 1, 690 p,p-Diaminodlpheny1methane (2.5).. 2, 240 o-Pllenylenediamine (5) 2,100 m-Phenylenediamine (5). Y 2,100 p-Pheuylenediamine (5) 2,200 N,N'-bis(mcthylhexadecyl)phenylenediaminc (5)... 2, 200 N ,N '-dlbenzyl-p-phenylenediamine (5) 950 1 The ozone exposure test was conducted at 40 C. with the samples being exed 30 times per minute from 0 to 20% elongation. With each group of compounds a control sample was included to serve as a monitor for thc group. The ozone concentration and times of exposure were regulated so as to obtain easily measured ozone cracking for comparativeurposes for each group of samples.

3 PBNA denotes phenyLbeta-naphthylamine. l

4 Flectol H is the condensation product of acetone and aniline..

5 Santoex B is the condensation product of acetone and p-ammodlphenyl.

Table II tabulates the tensile properties, hours expos- Santoex AW, and are represented by ythe formula ure, conditions of test and depth of ozone cracks under 60 R-HN--A-NHR, in which A is p,pbipheny1ene or dynamic test, for the controls, for compounds including methylenediphenylene, and one or both of R and R are the new antiozidants of the present invention, and for alkyl groups Containing g to .13 capbons, eg., samples other additives tested for comparative effectiveness. 9 and 11 0f'1ab1e 11` It was noted that when at least one of the N-radical Data for specimens prepared from 1101" GR S (GR substituents of p-phenylenediamine are secondary alkyl 65 1002) were Very simar to those for cold GR-S set groups the antiozidam activlty 1S more effectlve tha? forth in Table II and have therefrom been omitted for when such radicals are primary alkyl groups as exemplithe sake of brevity.

fied by samples 5 and 6 of Table II. Also when such radicals are lower alkyl groups as in Example 3 of Table II ozone protection is not afforded in dynamic tests 0f 70 heat aged elastomer compounds, in spite of the fact that Product- The Compoundmg recipe 1S aPPEIIed H1 h 1S such compounds are good antioxidants' table, and 1 t will be noted that PBNA was lncluded 1n In comparative studies a few specific compositions of the COIUPOUIldmg feClPe t0. fende? the results dlfeCtly matter were discovered jointly by the applicant and R. G. comparable with those obtained with GR-S.

Spain, which new compositions were more effective than 75 The ozone cracking in the case of the controls was in Table III illustrates the effectiveness of the new antiozidants in producing an ozone resistant natural rubber l 3 excess of the 50 microns A value which represents virtual immunity to ozone attack, while the natural rubber compounded with the 'new antiozidant of this invention was Well under that permissible A value.

lei respect to static elastomer samples; the tests being made on GR-S 1500 as well as on other elastomers not customarily used for tires or other articles which are subjected to dynamic stressing. ln these tests the ozone Table II COMPOUNDS OF GR-S 1500 SYNTHETIC RUBBER; AGED 24 HRS. AT 100 C OZONE EXPOSURE: 25:1:5 P.P.H.M. 40 C Sample Additive: pts/100 pts.

Tensile properties Ozone exposure Unaged Aged A VValue" Hrs crack Tens., Elong., Tens., Elong., depth p.s.i. Percent p.s.i. Percent (microns) 7 UZOP. Sample No. 2302-229 (Universal Oil Products sample)" s Tennessee Eastman Chemical Products, Ine* Samples prepared at applicants request and identity confirmed by elemental analyses.

NOTE A.-The octyl groups in the additive in Sample 6 are primary alkyl groups.

No'rn B.-The additive of Sample 6 is a new compound prepared and investigated by the applicant herein, and those of Samples 9 and 11 are new compounds discovered and investigated jointly by applicant W'th R.

G. Spain; each of which of these compounds appears superior to Santoiiex AW for protection against ozone. They are not as eiective for protection against ozone as the di-alkyl substituted p-phenylenediamine of which at least one alkyl is secondary, and in which the two alkyl radicals between them contains from 16 to 26 carbon atoms.

Table Ill DYNAMIC OZONE TEST [Compounded natural rubber lzlclme exposure: 255: p.p.h.m. @40 C;

Table IV shows the effectiveness of ozone protection afforded by antiozidants of the present invention with resistance is measured by the number of hours of ozone exposure required to produce microscopic cracking (ASTM rating 1) and the number of hours exposure required to produce severe visible cracking (ASTM rating 4).

A simple comparison with the control containing Santoilex AW as normally used, shows the outstanding superiority of the new antiozidants.

Similarly, comparison of the protected and unprotected Hycar, Philprene and BS/S/AA (butadiene/styrene/ acrylic acid terpolymer) further demonstrates the extreme eiectiveness of the new antiozidants.

Examples IV-l4 is which the total carbon atoms of the two alkyl substituents on the p-phenylenediamine exceeds 26, and in which the results were not even equal to those with the Santotlex AW control, Ifurther demonstrates the critical nature of the number of carton atoms in these substituents in which the sum total of carbon atoms must lie within the range of 16 to 26.

From the table it will be noted that the addition of from 1 to 5 parts of the new antiozidant increases the time preceding appearance of the rst ozone cracks in static samples, as much as thirty-fold over the time of appearance of irst cracks in synthetic rubber articles which have been prepared according to the best manner available prior to the 4discovery of the'new antiozidants set forth herein (see Table IV).

p l l o Table l V COMPUNDS AF SYNTHETIC ELASTOMERS STATIO OZONE TEST; :1;5 P.P.H.M. OZONE; 40 C Unaged Aged Sample Elastomer Additive: pts. per hundred elastomer Hr. at Hrs. at Hrs. at Hrs. at 0 rating 4 rating 0 rating 4 rating GR-S 1500-. Control with Santofiex AW, 2 pts 5 67 1 63 GR-S 1500.. N,Ndisecnonylp-phenylenediamine, 5 pt 2, 400 1 2, 400 2, 400 1 2, 400 GR-S 1500-. N ,Ndisecoctylpphenylenediamine, 5 pts.. 2, 400 1 2, 400 2, 400 1 2, 400 GR-S 1500-. N,Ndisecdodecylppl1enylenediamine, 5 pts. 2, 000 1 2,000 2,000 1 2, 000 GR-S 1500.. N,Ndisecundecylp-phenylenediamine, 5 pts 2, 000 1 2,000 2,000 1 2, 000 GR-S 1500.. N ,Ndi\ cocty)l-p,pdiaminodiphenylene-methane, 5 1,000 1 1,000 1,000 1 1,000

pts. ote

GR-S 1500.. N,Ndisectridecylp-phenylenediaminc, 5 pts 1,000 1 l, 000 2 1, 000 1, 000 GR-S 1500.. N -sec-octylbenzidine, 5 pts. (See N Ote A) 1, 000 1 1,000 1, 1, 000 Hycar 3.. No additive-Control 5 15 Hyoar N,N-di-see-nonyl-p-phenylenediamine, 5 pts. 754 2,100 Philprene 4.. N o additive-Control 5 270 1 267 Philprene..- N ,Ndi-see-nonyl-p-phenylenediamine, 2.5 pt 8 1. 000 BD/S/AA 5-. N ,Ndi-sec-octyl-p-phenylenediamine, 3.5 pts. 2,000 1 2, 000 2,000 1 2, O00 GR-S 1500-. N,N'-di-sec-heptadecyl-p-phenylenediamine, 3 p 3 24 12 4 Philprene is a butadiene/methylvinylpyridne elastomer (S5/15 weight ratio) 1 BDlS/AA is a terpolymer comprising, by weight 75 pts. butadiene/23 p NOTE L -The additive oi Sample 6 and of Sample 8 are new compounds discovered and investigated jointly by applicant with R. G. Spain.

FURTHER DISCUSSION As above noted it has been found that when the N,N hydrocarbon substituents on the p-phenylenediamine contain less than 16 or more than 26 carbon atoms the virtual immunization against ozone is not obtained (Examples II-3 and IV-14). It is applicants hypothesis that migration of the antiozidant is necessary to prevent ozone crack initiation at the air-rubber interface, and that the ability of the antiozidant to migrate is curtailed when the number of carbon atoms constituting the N,N-substitu ents is in excess of 26, and further that when the number of carbon atoms in such substituents is less than 16 the additives are lost by volatilization from heating or simple aging, and thus cannot protect the product. However, regardless of the mechanism of protective action or the reasons therefore, p-phenylenediamine derivatives, in which the hydrocarbon substituents contain not less than 16 or more than 26 carbon atoms, and at least one of which substituents is an alkyl group on one of the nitrogens, represents the class of compounds which are eiective as antioxidants.

To illustrate the observed critical nature of the number of carbon atoms in the alkyl substituents, and to show how such observed data fits the above hypothesis, there is presented herewith a diagram (FIGURE l) showing the virtual immunity of GR-S 1500 type synthetic rubber protected from ozone cracking by 5 parts RHNONHR when the number of carbon atoms in R+R of the formula (in which R and R are hydrocarbon radicals and at least one of them is a secondary alkyl radical) is at least 16 and not more than 26. In this diagram an A value of 50 or less represents critical immunity from ozone attack; while at an A value above 500, the samples usually break during the dynamic testing and thus cannot be subjected to a full period of dynamic testing. When A values are obtained that lie from above 50 to about 500 the specimens can be fully tested to afford comparable data on crack depth, but the ozone protection is poor. The line X represents the loss yof immunity to ozone attack after aging when the antiozidant is lost by volatilization; the line Y represents the loss of immunity to ozone attack when the molecular weight of the substituents is too great and the ability of the antiozidant .to migrate to the surface is lost.

ts. styrene/2 pts. acrylic acid.

As stated above, data for hot GR-S (polymerized at 122 F. instead of 41 F. used for the cold GR-S) compounded with the new antiozidants were also obtained and were found to be practically identical with data for cold GR-S. The GR-S elastomers are considered to be neutral nonpolar elastomers. Hycar (18% acrylonitrile) was used to represent the class of neutral polar elastomers; since it consists of a copolymer of butadiene and acrylonitrile it contains the polar nitrile groups. As a representative of basic polar elastomers, a copolymer of butadiene and a methylvinylpyridine (Philprene VP) was tested with and without the new antiozidants. Further, an elastomer comprising a copolymer of butadiene-styrene-acrylic acid in the weight ratio of 75/23/2 was used to represent the class of acid polar elastomers. Comparison of the results attained, mutually and with the controls, shows that all four types of elastomers are highly protected against ozone by incorporation of three to ve parts of the new antiozidants therein; and the same considerations show that natural rubber is similarly protected.

In addition to the examples given in the tables copolymers of styrene and butadiene were prepared which contained small amounts of copolymerized carbnoylcontaining monomers such as methylvinylketone, crotonaldehyde or methyl isopropenylketone and compounded with the antiozidants of this invention, and the results showed that these antiozidants are useful as additives for these carbonyl containing elastomers.

These and other elastomers may be employed as additives, e.g., plasticizers for plastomer products, for which polar elastomers are usually selected. In such cases ozone deterioration of the elastomer component is prevented bythe antiozidants of this invention.

The samples shown in the tables cover the ve principal types of elastomers, above described, but the range of elastomers, and plastomer combinations, protected against ozone attack by the present antiozidants is not limited thereto, as similar results have been obtained with other elastomers e.g., polybutadiene, butyl rubber, neoprene, etc. As also noted above, the GR-S 1500 used in the many examples in Tables I, II and IV contained antioxidant material capable of withstanding vulcanization, usually PBNA. Such antioxidant materials notably PBNA afford no protection against ozone attack of the principal products, nor do they enable the other antioxidants of Table I to do so. From certain of the observed data, however, it appears that in combination with the new antiozidants, the PBNA and similar anti- 17 oxidant materials may have a synergistic eect enabling smaller quantities of the antiozidanits of the present invention to effectively proect the products against ozone attack.

Variations in compounding of the elastomers can nullify the protective action of these antiozidants. For example, high amounts of waxes, plasticizers or stearic acid lower the eiectiveness of our new additives in rubbers. Caution should be exercised by the compounder to avoid excessive amounts of such ingredients particularly Where the elastomer is subjected to dynamic use.

In general lrom 0.5 to 5 pants vof antiozidant per hundred of rubber is adequate for practice of the invention in protection of natural and synthetic rubbers against deterioration due to ozone attack.

These antiozidants have also been found to be effective in protection against ozone cracking of plastomers which have residual unsaturation or active hydrogens such as may be present in methylene or methinyl groups. Thus resins or plastomer compositions comprising polymers and copolymers of vinylchloride, vinylacetate, alkylacrylates, etc., in combination with unsaturated polymer ingredients, are subject to attack by ozone, and such attack is avoided when the new antiozidants are present in such compositions.

These new antiozidants have also been found eiiective in protection of elastomer dispersions such as latices of natural rubber, GR-S elastomers, neoprene, acrylonitrile copolymeric elastomers, and the like which are to be used for coating and nlm-forming purposes, e.g. for paper coatings, wall paints, etc. By incorporation References Cited in the tile of this patent UNITED STATES PATENTS 1,550,749 Shafer Aug. 25, 1925 2,323,948 Von Bramer et al. July 13, 1943 2,384,141 Soday Sept. 4, 1945 2,435,246 Strain Feb. 3, 1948 2,435,411 Soday Feb. 3, 1948 2,498,630 Thompson Feb. 28, 1950 2,734,808 BisWell Feb. 14, 1956 2,779,789 Rosenwald et al. Jan. 29, 1957 OTHER REFERENCES Shaw et al.: Rubber World, vol. 130, No. 5, pages 636 to 642. 

